Centrophorus granulosus (Bloch & Schneider, 1801)

Alkusairy, Hasan & Saad, Adib, 2018, Species Composition, Diversity and Length Frequency of By-Catch Sharks from the Syrian Coast, International Journal of Research Studies in Zoology 4 (1), pp. 11-21 : 17-20

Centrophorus granulosus

TL ranged between 46 and 97 cm for males and between 46 and 105 cm for females. Common TL ranged from 77 to 85 cm for males and from 80 to 90 cm for females. C. granulosus was recorded in all months of years. Females constituted 59.6% of species catches. A significant difference between caught seasons was founded (X 2 = 15.915, P = 0.001), peak of season and juveniles landing were in summer ( Fig. 2h and Fig. 3h ). [ 21] reported that males and females of C. granulosus matured at 80 and 90 cm TL, respectively. Consequently, about 37% of males and 68% of females were immature in species catches ( Fig. 4h ).

There were three possible nursery areas for H. griseus (northern Ras Albassit, northern Lattakia and northern Tartous) in Syrian marine waters. Moreover, three possible nursery areas were in the region for C. plumbeus (one area southern Lattakia and two areas southern Tartous). While there were two possible nursery areas for M. mustelus (against Lattakia and middle distance between Jablah and Banias) ( Fig. 5 ).

The very economically important species being caught in plentiful quantities and highly consumable: C. plumbeus , M. mustelus C. uyato , H. griseus , and S. blanvllei . Moderate economically important species either for being caught in little quantities with high efforts in fishing, or for their little demand for human consumption, or may be both reasons: H. perlo , I. oxyrinchus , A. superciliosus , C. obscurus , D. licha , S. squatina , S. oculata , S. aculata , in Syrian marine waters [ 2].

The seasonal variation findings are in agreement with [ 22] Buencuerpo et al. (1998) and [ 23] Megalofonou (2005), who reported maximum catch rates in April (spring) and September (autumn). Certain water temperature preferences of sharks force them to shift to deeper, cooler water masses, especially in tropical and subtropical areas. In these depths they are less vulnerable to surface longlining and that reflects in lower catch rates [ 24, 25, 26, 27].

The two pelagic species H. griseus (common), C. plumbeus (abundant) and the deep-water species M. mustelus (common) fishery were dominance by juveniles, which considered as vulnerable, endangered and endangered, respectively, on regional Red List of Mediterranean Sea. These species were occurrence every month round year that totally composed about 25% of Syrian sharks landing. The females catches of the pelagic species H. perlo (common), also the three deep-water species S. blainvillei (abundant), C. uyato (common) and C. granulosus (common) were mostly comprised by juveniles. Which considered as vulnerable, data deficient, unknown and vulnerable, respectively, on regional Red List of Mediterranean Sea. Conversely, catches of the deep-water species G. melastomus was comprised by a little numbers of juveniles in both sexes. The presence of recruits both between 200 and 650 m, a greater percentage of mature individuals in the mesobathyal than in epibathyal and homoeothermic condition in the bathyal environment of Mediterranean, this may cause by that the reproduction occurs at the lowest depths at which the species is found. More ever, the use of longlining scatter baits made them more accessible to smaller species [ 2]. The low percentage of G. melastomus recruits caused by discarding of small individuals after catch immediately because of it has no economical important.

In addition, the investigations with fishermen showed a major decline in the quantity (number and size of individuals) of shark fishery throughout last ten years, this situation caused by overfishing with the historical life characterizes of shark, represented by; large size at maturity, slow growth rate and low fecundity. These reasons make this fish group suffering from disability to complete its life cycle, as result a high proportion of juveniles were found in its catches, reached to 83%-100% for three species. [ 28] reported that there is increasing evidence that indirect effects of fishing are affecting the composition and diversity of chondrichthyan and total fish assemblages through trophic interactions, so we have to set up a monitoring program for chondrichthyan fishery and its landing.

Figures

Figure 2. Changes of caught specimens number per season; (a) H. griseus,(b); H. perlo, (c); C. plumbeus, (d); M. mustelus (e); G. melastomus, (f); S. blainvillei, (g); C. moluccensis, (h); C. granulosus

Figure 3. Size (TL) variations of abundant and common of by-catch sharks per season off Syria coast. Males (gray), females (white): (a); H. griseus,(b); H. perlo, (c); C. plumbeus, (d); M. mustelus (e); G. melastomus, (f); S. blainvillei, (g); C. granulosus, (h); C. uyato

Figure 4. Total length (TL) frequency distributions (percent of species catch) of the abundant and common bycatch sharks off Syrian coast. Males (black), females (white). Vertical lines indicate maturity size of males (sporadic) and females (continuous) following literature: (a); H. griseus,(b); H. perlo, (c); C. plumbeus, (d); M. mustelus (e); G. melastomus, (f); S. blainvillei, (g); C. granulosus, (h); C. uyato

Figure 5. Geographic distribution of possible nursery areas for three species (H. griseus; +, C. plumbeus; ×, M. mustelus; *, black circles; main cities) in Syrian marine waters.